1. Field of the Invention
This invention relates to a process and apparatus for separating particulate solids from a gaseous process fluid in a pressurized materials processing system. The invention also contemplates conserving and/or recycling the major portion of the gaseous process fluid for both energy conservation and economy of operation. Specifically, the invention has particular application to pulping systems used in the pulp, paper and board (fiberboard, hardboard, particleboard, chipboard, etc.) industries.
2. Description of the Prior Art
In, for example, the processing of lignocellulose pulp from wood chips, sawdust, rejects, semi-chemically cooked chips, etc., under conditions of full steaming tube or digester pressure, e.g., pressurized or thermomechanical refining, it has been the practice over the years to separate the refined pulp or fibers from the steam (or essentially steam) processing fluid at atmospheric pressure. This was generally accomplished by means of a single cyclone separator or other material separator apparatus, such as that disclosed in applicant's U.S. Pat. No. 4,253,857, assigned to the assignee of the present invention and herein incorporated by reference.
However, with the advent of a more recent interest in or demand for the use of higher pressure steam refining of lignocellulose pulp, e.g., up to 180 p.s.i.g. or higher, the need for an approach other than the use of an atmospheric cyclone separator or applicant's aforesaid patented separator became evident. Moreover, it has become evident that any newly developed technology for fulfilling such desiderata should be energy efficient.
Notwithstanding, the approaches heretofore offered as a solution to the above problem involved considerable additional apparatus and expense, in addition to process control or balancing problems. Some of such prior approaches included, inter alia, using cyclone separators in series, pressure vessels, rotary valves, plug dischargers, high density pumps, gear pumps, compressor screw feeders, cell feeders, or the like in various combinations with the basic pressurized or thermo-mechanical pulping apparatus. Typical examples of some such approaches are disclosed in U.S. Pat. Nos. 4,136,831 and 4,235,665, among others.
A need has therefore arisen for an improved process and apparatus for economically and efficiently separating fiber from steam or the like in a pressurized or thermo-mechanical pulping system and, in addition, such a process and apparatus that is also energy efficient.